1. Field of the Invention
This invention relates to a new electrochromic material, a method of making the new electrochromic material, and an electrochromic device utilizing the new material.
2. Description of the Related Art
In order to better understand my inventive contributions, I will first undertake a general discussion of electrochromic behavior in electrochromic materials. Electrochromism is a coloring phenomenon observed in some materials when they are placed in the presence of an electrical field. Such materials are normally uncolored when no electrical field is present, but change to a colored state when an electrical field is placed therearound.
Such a material exhibiting reversible color changes is known as an electrochromic material (ECM). This electrical field dependent transition phenomenon from an uncolored state to a colored state is called optical switching. If a thin coating of such an ECM is placed on a glass support, the entire device is known as a switchable window. When no electrical field is placed on the ECM, it is uncolored and transparent and thus one can look through the window. On the other hand, when an electric field is placed on the ECM, it colors thereby reducing the amount of light transmitted through the window. The reduction of light transmission may be partial or total thereby either reducing the amount of light which passes through the window or eliminating it altogether.
Certain transition metal oxides are known to exhibit electrochromism. Materials such as tungsten oxide, molybdenum oxide, and vanadium oxide are known electrochromic materials.
Electrochromic materials can be divided into two categories depending on the mode of operation of the ECM. The ECM can be either a cathodic ECM or it can be an anodic ECM. The operation of these two types of ECM will be understood by reference to FIGS. 1 and 2.
In FIG. 1, the operation of a cathodic ECM is schematically illustrated. In the cathodic case, an electrochromic material of the cathodic type is physically located next to a cathode which has been placed, for example, on a glass substrate. A fast ion conductor material, which Produces light ions of a positive charge, for example, lithium ions, is placed between the electrochromic material and an anode which also may be placed on a glass substrate.
In the cathodic case, the electrochromic material is subjected to a reduction or gain of electrons when an electric field is applied thereto. Application of the electric field is indicated by the plurality of plus signs shown on the anode and the plurality of negative signs shown on the cathode. As a result of the application of an electric field applied between the anode and the cathode of appropriate strength and sign, positive light ions are driven from the fast ion conductor into the electrochromic material and electrons are supplied to the electrochromic material from the cathode.
The positively charged light ions and the negatively charged electrons associate themselves with the electrochromic material to reduce the same thereby moving the electrochromic material from a base state to a reduced state. In the base state, the electrochromic material is uncolored, but in its reduced state, it is colored.
When the electric field is removed, the electrochromic material will return to its base state, that is, its uncolored state. The period of time required for return of the material to its uncolored state varies from material to material and is generally referred to as the memory of the ECM. Some materials have relatively short memories and others have prolonged memories.
While the operation of the cathodic material has been illustrated by the inclusion in the electrochromic material of positive light ions and negative electrons, the cathodic operation may also take place by the extraction of negative light ions and holes from the electrochromic material respectively to the fast ion conductor and the cathode.
Operation of an anodic ECM is schematically illustrated in FIG. 2. In this case, the electrochromic material is located next to the anode and the fast ion conductor is located between the electrochromic material and the cathode. In the anodic operation, oxidation of the ECM takes place, that is, electrochromism occurs when the ECM loses electrons. The loss of electrons in this case is illustrated by the application of an electric field represented by a plurality of pluses on the anode and the plurality of minuses at the cathode.
In the case of an anodic ECM, when an electric field is applied between the anode and the cathode of appropriate strength and sign, negative light ions, such as hydroxyl ions, move from the fast ion conductor into the ECM, and holes moves into the ECM from the anode. As a result of this movement, the ECM loses electrons thereby being oxidized away from its base or uncolored state to a colored state. Once again, the anodic material will return to its base state when the electric field is released. The time of return to its uncolored state again depends on the memory of the ECM.
The anodic ECM may also operate by extracting from the ECM positive light ions and negative electrons respectively to the fast ion conductor and the anode. In this case, the ECM is also oxidized to a colored state.
In general, in either the cathodic ECM or the anodic ECM, the coloring observed in the material is an electrochemical phenomenon produced by the application of an electric field on the ECM to move it from a base condition to a nonbase condition. By applying a field of required strength and direction to cause activity in the ECM, polarization occurs within the entire electrochromic device. In such polarization, a disassociation of ions occurs in the fast ion conductor creating free light ions of the required charge. These light ions move into the ECM because of the electrical field. Once in the ECM, they bond themselves to the molecules of the ECM.
As has been described above, depending on the charge of the bonding ion and its associated electron or hole, oxidation or reduction of the ECM occurs. These ECM materials are normally multivalent state materials exhibiting different optical absorption and dispersion spectra corresponding to different oxidation states. For these ECM's, these different oxidation and reduction states are all stable under appropriate electric field conditions.
In the base ECM, the metal valance states are generally at the maximum, whereby such metal oxides in their base state exhibit the lowest optical absorption. They are generally good insulators with high energy gaps, optically transparent and colorless in such a condition. On the other hand, oxygen deficient oxides as well as reduced oxides created as a result of the application of an electric field exhibit higher optical absorption than those of base oxides When oxygen deficient, ECM's exhibit a selective absorption when they are in on of their other oxidation states Different ECM exhibit different colors, depending upon the spectral location of the selective absorption bands of that particular oxygen deficient metal oxide.
The explanation so far set forth above of cathodic and anodic ECM is my best explanation. It is possible to reduce this theory of mine to electrochemical equations in which a base ECM, acting as a cathodic material, would be subjected to a reduction by inclusion in the ECM of positive light ions and negative electrons or by extraction from the ECM of negative light ions and holes respectively to the fast ion conductor and the cathode in order to reduce the cathodic ECM to its colored state.
In a similar manner, an electrochemical equation may be written for an anodic ECM in the same manner. In this case, the inclusion of negative light ions and holes in the ECM or the extraction of positive light ions and negative electrons respectively to the fast ion conductor and the anode is sufficient to oxidize the anodic material to a colored state.
I personally conducted a search in the U.S. Patent and Trademark Office on the subject matter of this specification. As a result of that search, I uncovered only one patent which I felt was only remotely associated with the subject matter to be taught as the invention herein. The patent was U.S. Pat. No. 3,521,941, which issued July 28, 1970, for an "Electro-Optical Device Having Variable Optical Density". This patent, in column 4, line 7, mentions copper stannate as a possible electrochromic material.
It is an object of this invention to provide a new electrochromic material.
It is a feature of this invention that a new electrochromic material is provided which can be either an anodic ECM or a cathodic ECM.
It is an advantage of this invention that a newly provided ECM having both anodic and cathodic capabilities can be switched between an uncolored state and three distinct and different color states.
It is another object of this invention to provide an electrochromic device having a new ECM therein.
It is another feature of this invention that a electrochromic device can be constructed with a newly provided ECM having both anodic and cathodic capabilities, whereby the electrochromic device can be used as either an anodic electrochromic device or a cathodic electrochromic device, or both.
It is another advantage of this invention that an electrochromic device can be constructed using a newly provided ECM having both anodic and cathodic capabilities, whereby the electrochromic device can be switched between an uncolored state and three distinct and different color states.